1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine, which controls the internal combustion engine, and, more particularly, to the control that is executed at the time of purging vaporized fuel or fuel vapor, produced in a fuel tank, into the intake system of the internal combustion engine.
2. Description of the Related Art
Some internal combustion engines comprise fuel supply means for supplying fuel for generating power to the internal combustion engine, a fuel tank for retaining fuel to be supplied to the internal combustion engine by the fuel supply means, and purge means for purging fuel vapor, produced in the fuel tank, into the intake system of the internal combustion engine. Such an internal combustion engine is disclosed in, for example, Japanese Patent Application, First Publication No. Hei 8-338290.
In the conventional internal combustion engines, a correction amount for correcting the amount of fuel is incremented or decremented by a given amount. When the purge amount changes suddenly due to a change in the running state of the internal combustion engine, therefore, the correction of the amount of fuel corresponding to the purge amount may not be carried out adequately so that the exhaust component characteristic may deteriorate.
When the load varies while the internal combustion engine is idling, the fuel may not be corrected adequately while the purge amount changes in accordance with the change in the load. As a result, the air-fuel ratio becomes lean, making the running of the engine unstable.
When a large correction amount is updated while the internal combustion engine is idling, the running of the engine may become unstable due to a change in the amount of fuel supply. If the correction amount to be updated is made small, the correction cannot properly respond to the influence of purging when the internal combustion engine is in states other than the idle state. In this case, the exhaust component characteristic may deteriorate.
The control apparatus for the conventional internal combustion engine uses a purge cut solenoid valve (hereinafter referred to as a solenoid). The solenoid controls the amount of vaporized fuel or fuel vapor, produced in a fuel tank and to be supplied to the intake system, and calculates a purge correction coefficient for decreasing the amount of fuel to be supplied from an injector, thereby preventing the over-rich state in the cylinder.
As the vaporized fuel supplied into the cylinders is increased, the purge correction coefficient for the calculation of the correction purge amount is increased, and the amount of fuel to be supplied from the injector is decreased.
In this case, the purge correction coefficient is controlled depending on the opening degree of the solenoid.
When the factor of the purge correction coefficient for determining the updating amount of the purge correction amount is always fixed, there are the problems described below.
When the factor is set to be large, based on a high target air-fuel ratio, the output significantly varies while in a lean-burn state, in which the combustion is unstable, thereby degrading the driveability. When the factor is set to be small, based on a low target air-fuel ratio, the follow-up control for following the variation of the purging is degraded.
When the control apparatus fully closes the opened solenoid, the purge correction coefficient is immediately set to 0. Therefore, the vaporized fuel remaining between the solenoid and the intake manifold may flow into the cylinder, thereby causing an over-rich state.
Accordingly, it is an object of the present invention to provide a control apparatus for an internal combustion engine which can execute finer correction control of the fuel supply means for the purge amount of fuel vapor.
To achieve the above object, according to one aspect of this invention, there is provided a control apparatus for an internal combustion engine, which comprises an internal combustion engine; fuel supply means (fuel injection valves 12 in a preferred embodiment) for supplying fuel to the internal combustion engine; a fuel tank (fuel tank 41 in the embodiment) for retaining fuel to be supplied to the internal combustion engine by the fuel supply means; purge means (fuel vapor processing device 40 in the embodiment) for purging fuel vapor, produced in the fuel tank, into an intake system of the internal combustion engine; air-fuel ratio detection means (LAF sensor 17 in the embodiment), provided in an exhaust system of the internal combustion engine, for detecting an air-fuel ratio (real air-fuel ratio coefficient KACT in the embodiment); a target air-fuel ratio setting means (ECU 5 in the embodiment) for setting a target air-fuel ratio (target air-fuel ratio coefficient KCMD in the embodiment) in accordance with the running state of the internal combustion engine; update amount setting means (determination in step S407 and processes of steps S422 and S423 all performed by the ECU 5 in the embodiment) for setting the update amount (update amount DKEVACT in the embodiment) which becomes larger as a deviation between the air-fuel ratio detected by the air-fuel ratio detection means and the target air-fuel ratio becomes larger; and purge correction amount updating means (processes of steps S023 and S025 performed by the ECU 5 in the embodiment) for updating a purge correction amount (purge correction coefficient KAFEVACT in the embodiment) for correcting an amount of fuel (fuel injection time TOUT in the embodiment) with the update amount set by the update amount setting means.
With the above structure, when a deviation between the real air-fuel ratio and the target air-fuel ratio is large, the update amount setting means sets a large update amount with which the purge correction amount updating means updates the purge correction amount for correcting the amount of fuel. Even when the purge amount changes drastically due to a change in the running state of the internal combustion engine, therefore, correction of the fuel amount corresponding to the purge amount is carried out properly. This prevents the exhaust component characteristic from deteriorating.
According to another aspect of this invention, there is provided a control apparatus for an internal combustion engine, which comprises an internal combustion engine; fuel supply means (fuel injection valves 12 in the embodiment) for supplying fuel to the internal combustion engine; a fuel tank (fuel tank 41 in the embodiment) for retaining fuel to be supplied to the internal combustion engine by the fuel supply means; purge means (fuel vapor processing device 40 in the embodiment) for purging fuel vapor, produced in the fuel tank, into an intake system of the internal combustion engine; idle determination means (determination in step S401 by the ECU 5 in the embodiment) for determining whether the internal combustion engine is in an idle state or not; load change detection means (determinations in steps S403 and S404 by the ECU 5 in the embodiment) for detecting a change in a load of the internal combustion engine; and purge-correction-amount initialization means (processes of steps S406, S023 and S025 performed by the ECU 5 in the embodiment) for initializing a purge correction amount (purge correction coefficient KAFEVACT in the embodiment) for correcting the amount of fuel (fuel injection time TOUT in the embodiment) when the idle determination means has determined that the internal combustion engine is in the idle state and the load change detection means has detected a change in the load.
With the above structure, when the idle determination means has determined that the internal combustion engine is in an idle state and the load change detection means has detected a change in the load, the purge-correction-amount initialization means initializes the purge correction amount for correcting the amount of fuel. In the case where the load varies in the idle state, even when the purge amount varies in accordance with the change in the load, the fuel amount can be corrected adequately to prevent the air-fuel ratio from becoming lean. This prevents the running of the engine from becoming unstable.
According to a further aspect of this invention, there is provided a control apparatus for an internal combustion engine, which comprises an internal combustion engine; fuel supply means (fuel injection valves 12 in the embodiment) for supplying fuel to the internal combustion engine; a fuel tank (fuel tank 41 in the embodiment) for retaining fuel to be supplied to the internal combustion engine by the fuel supply means; purge means (fuel vapor processing device 40 in the embodiment) for purging fuel vapor, produced in the fuel tank, into an intake system of the internal combustion engine; idle determination means (determination in step S401 by the ECU 5 in the embodiment) for determining whether the internal combustion engine is in an idle state or not; update amount setting means (processes of steps S409, S414, S420, S422, S423, S427, S429, S432, S434 and S435 performed by the ECU 5 in the embodiment) for setting a update amount smaller/lower?? when the internal combustion engine is in the idle state than when the internal combustion engine is not in the idle state; and purge-correction-amount updating means (processes of steps S023 and S025 performed by the ECU 5 in the embodiment) for updating a purge correction amount (purge correction coefficient KAFEVACT in the embodiment) for correcting the amount of fuel (fuel injection time TOUT in the embodiment) with the update amount set by the update amount setting means.
As apparent from the above, when the idle determination means has determined that the internal combustion engine is in an idle state, the update amount setting means sets a update amount so as to be smaller when the internal combustion engine is in the idle state than when the internal combustion engine is not in the idle state, and the purge-correction-amount updating means updates the purge correction amount with that update amount. As the update amount is made smaller when the internal combustion engine is in the idle state, the running of the engine will not become unstable. As the update amount is made larger when the internal combustion engine is in states other than the idle state, the correction can properly respond to the influence of purging so that the exhaust component characteristic will not deteriorate.
It is therefore another object of the present invention to provide the apparatus which can appropriately determines the amount of fuel to be supplied, depending on the driving condition and the target air-fuel ratio.
To achieve the above object, the control apparatus for an internal combustion engine of the present invention comprises: a purge device (the passage 42, the purge passage 43, the purge control valve 44, the canister 45, the two-way valve 46 in the embodiment) for purging fuel vapor, produced in a fuel tank (the fuel tank 41 in the embodiment), into an intake system of the internal combustion engine (the engine body 1 in the embodiment); a purge correction amount calculator (steps S003, and S039 to S043 executed by the ECU 5 in the embodiment) for calculating the purge correction amount for decreasing the amount of fuel to be supplied to the internal combustion engine, depending on the amount purged by the purge device; a target air-fuel ratio setting device (the ECU 5 in the embodiment) for setting a target air-fuel ratio in accordance with the running state of the internal combustion engine; an air-fuel ratio correction amount calculator (the ECU 5 in the embodiment) for calculating an air-fuel ratio correction amount for adjusting the air-fuel ratio of mixture to be supplied to the internal combustion engine to the target air-fuel ratio set by the target air-fuel ratio setting device; an update amount setting device (steps S053 to S065 executed by the ECU 5) for setting the update amount of the purge correction amount, depending on the target air-fuel ratio set by the target air-fuel ratio setting device; and a fuel supply amount determining device (the ECU 5) for determining the amount of fuel to be supplied to the internal combustion engine, depending on the purge correction amount, updated based on the update amount determined by the update amount setting device, and on the air-fuel ratio correction amount.
With the above structure, the update amount calculator determines the update amount of the purge correction amount, depending on the target air-fuel ratio set by the target air-fuel ratio setting device. When the actual air-fuel ratio is leaner than the target air-fuel ratio, the update amount of the purge correction amount is changed/updated/corrected/???? gradually, thereby preventing a decrease in the engine speed and the engine stop due to the over-lean state.
In another aspect of the present invention, the purge correction amount calculator gradually decreases the correction amount when stopping the purging.
With the above structure, when executing the purge cutting, the decreasing correction value for decreasing the amount of fuel to be supplied to the internal combustion engine is not immediately set to 0, and gradually becomes 0], thereby preventing the rich-state of the actual air-fuel ratio due to the fuel vapor remaining in the system.